the basic definition for being "that guy" is to just be as annoying as humanly possible at any and all types of social functions, and annoying in many different ways,
examples can include drinking too much and pissing your pants/vomiting, hitting on girls that are most def not interested in you, telling ridiculous stories that are
obvious lies, and many other crazy ridiculous things. You most definitely do not want to become "that guy".

Guy 1: Not bad in here tonight (in a bar/club).
Guy 2: Yeh, good amount of women in here, and the drink specials actually drinks we can enjoy.
Guy 3: Dude I def have my eyes on that hottie over there (points)
"That Guy": Yo, wazzup guys (annoying prolonged wazzup) this is my 4th shot and I already had 5 beers also!
Guy 1: Wow I dont care how much I have to drink, why would I care about how much you have??
Guy 2: Yeh you really are "That guy".
Guy 1 & 3: Yeh seriously, get lost you loser.
"That Guy": Sorry guys, I wont bother you again.

"That Guy": (Shouting as loud as he can to be heard over music at house party) Alright I am leaving to go to (insert crappy bar name here)!
Rest of Party: Alright later, (thinking thank the good lord he is leaving)
"That Guy": (Still shouting but music shuts off to start another song) Gonna try and get laid !!
Rest of Party: HAHAHAHA, yeh good luck man, LOSER!
"That Guy": (out in his car thinking) Wow, I really am that guy.